Device for disinfecting medical materials

ABSTRACT

A device for disinfecting medical materials includes a heat source capable of heating the medical materials to approximately 60° C. and exposing the medical materials to a source of gamma irradiation capable of irradiating medical materials with about 0.25 to about 2.0 Mrads.

This is a continuation of application Ser. No. 07/530,438, now U.S. Pat.No. 5,035,858, filed on Jun. 1, 1990, which is a continuation ofapplication Ser. No. 07/421,332 filed on Oct. 13, 1989, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates generally to a device for disinfectingmedical materials and more particularly to a device for disinfectingmedical materials by exposing the materials to a combination of heat andgamma radiation. The term medical materials encompasses medical waste,veterinary waste and medical products. The problems with current wastehandling methods will be discussed first.

The problem of disposal of solid waste is becoming increasingly acute.The primary methods of solid waste disposal have been burning or burialin landfills. These two methods have severe disadvantages. Burningliberates waste particles and fumes which contribute to acid rain.Burying wastes results in toxic chemicals leaking into the surroundingearth and contaminating the water supply. Although increasing amounts ofsolid waste are being recycled, which alleviates the problems of theother two disposal methods, presently available recycling methods do notprovide a complete solution to the disposal problem.

Waste disposal is of even more urgent concern when the waste may causeinfection. Such infectious waste is a by-product of medical andveterinary care. For example, regulated medical waste consists of thefollowing categories:

1. Cultures and stocks of infectious agents and associated biologicals,

2. Pathological wastes,

3. Human blood and blood products,

4. Contaminated sharps (including needles, syringes, blades, scalpels,and broken glass),

5. Animal waste,

6. Isolation waste (gloves and other disposable products used in thecare of patients with serious infections), and

7. Unused sharps.

These wastes can be generally divided between general medical waste,including waste listed above in categories 1, 2, and 3; veterinarywaste, or category 5; and waste that is predominantly plastic, includingcategories 4 and 6. Hospitals typically segregate types of waste.Contaminated sharps and isolation waste are categories of specialconcern, as this waste may carry highly dangerous infections such asAIDS or hepatitis. Sharps in particular have caused public panic whenobserved on beaches and other public areas.

Hospitals and other generators of medical and veterinary waste employthree main methods of waste handling: 1) on-site incineration of thewaste, 2) on-site steam autoclaving of the waste and later shipment to alandfill, and 3) no on-site processing before turning the waste over toa waste hauler.

Predominantly located in urban areas, many hospital incinerators emitpollutants at a relatively high rate. In the emissions of hospitalincinerators, the Environmental Protection Agency (EPA) has identifiedharmful substances, including metals such as arsenic, cadmium, and lead;dioxins and furans; organic compounds like ethylene, acid gases, andcarbon monoxide; and soot, viruses, and pathogens. Emissions from theseincinerators may be a bigger public health threat than improper dumping.(Stephen K. Hall, "Infectious Waste Management: A multi-facetedProblem," Pollution Engineering, 74-78 (Aug. 1989)).

Although steam autoclaving may be used to disinfect waste before furtherprocessing, it is expensive and time-consuming. Temperature monitoringdevices such as thermocouples and biological indicators such asheat-resistant Bacillus stearothermophilus spores may be used to assureeffective disinfection. The application of heat denatures the protein inmicroorganisms causing death in a short time. Viruses are rapidlyinactivated; bacteria and particularly bacterial spores survive somewhatlonger than viruses.

U.S. Pat. No. 2,731,208 (Dodd) teaches a steam-sterilizing apparatus fordisposing of contaminated waste which incorporates shredding the waste("including paper containers such as used sputum cups," Col. 1, Lines28-29). This reference teaches processing only limited types of items;it teaches the use of steam sterilization alone and has the furtherdisadvantage of depositing the shredded mixture into a sewer. (Col. 4,line 49).

Whether or not the hospital first autoclaves its medical waste,including broken needles and glass, the waste is then turned over to awaste handler for transport to a landfill or other depository. U.S. Pat.No. 3,958,936 (Knight) teaches compaction of hospital waste for moreefficient landfill disposal. Specifically, this reference teaches theapplication of heat in the range of about 400° to 600° F. to hospitaland other waste to melt the plastic and turn it into a hard, compactblock for safer disposal in landfills. The waste is disinfected andneedles become imbedded in the plastic. This method has thedisadvantages of requiring high temperatures and landfill disposal. Asmentioned above, metropolitan landfills are becoming filled andunauthorized dumping is becoming a problem.

Another area of concern is the sterilization of medical products. Bymedical product we mean any product which must be disinfected orsterilized prior to use in patient or animal care. This area isexemplified by, but not limited to, the following: needles, syringes,sutures, scalpels, gloves, drapes, and other disposable items. Manyreusable items also must be provided in sterile form. Primarysterilization methods include the use of autoclaving, ethylene oxide,and ionizing radiation. The heat and humidity of autoclaving are quitedamaging to many disposable medical products; hence autoclaving is notpreferably used, and ethylene oxide and ionizing radiation are preferredcommercially.

To sterilize medical products with known methods, poisonous ethyleneoxide gas fills a closed chamber containing the products to besterilized. For effective sterilization, not only must the ethyleneoxide concentration be carefully controlled, but the temperature,humidity and porosity of the sterilizer load also must be regulated.Ethylene oxide is slow to dissipate from plastics and may require thatthe medical products be stored until the ethylene oxide falls to a safelevel. Ethylene oxide also must be carefully vented to the atmosphereafter the sterilization cycle to avoid poisoning workers.

If ionizing radiation such as gamma radiation is used by itself, it mustbe administered at such intense doses that many plastics become yellowand brittle. For example, U.S. Pat. No. 3,940,325 (Hirao) teaches waysto adjust the formulas of plastics for syringes to avoid yellowing andcracking after exposure to gamma radiation. Other substances may also bedamaged by radiation.

Ionizing radiation, or gamma radiation, is produced by electronaccelerators or radioisotopes such as cobalt 60 or cesium 137. Bothsources produce high-energy photons which disinfect by inactivating theDNA of viruses and bacteria. These irradiated microorganisms lose theirability to reproduce and cause infections. Gamma radiation rapidlyinactivates bacteria but is less effective against viruses. On alarge-scale industrial basis, gamma irradiation with cobalt 60 has beenused to sterilize medical products prior to their use in patients. Thedosage of gamma radiation, measured in rads or megarads (Mrads), variesbut a dose of 2.5 Mrads is usually selected as a starting point in knownmethods. However, such doses also damage the product being sterilized.The following patents teach methods to sterilize medical products withless harm to the product.

U.S. Pat. No. 3,617,178 (Clouston) teaches a method of improvingsterilization efficiency by increasing hydrostatic pressure. Elevatedhydrostatic pressure causes sterilization-resistant bacterial spores togerminate or begin to grow, but it has no effect on viruses. Germinationmakes the bacteria more sensitive to radiation. This reference teachesoptimizing the hydrostatic pressure effect by adjusting temperature (upto 80° C.), and then disinfecting the sutures with lower doses of gammaradiation or other modes of disinfection. According to Clouston,elevated pressure and fluid or moist gas are essential to his method;raised temperature alone has a negligible effect. Furthermore, thepressure/heat/moisture treatment this reference teaches is intended tocause bacterial spores to germinate, not to immediately sterilize orinactivate microorganisms.

In contrast, U.S. Pat. Nos. 4,620,908 (Van Duzer) and 3,704,089(Stehlik) teach pre-freezing injectable proteins and surgical adhesiverespectively before irradiation with cobalt 60. In these methods, thetemperature is reduced not to sterilize the product, but to protect theproduct from damage by gamma radiation.

U.S. Pat. No. 3,602,712 (Mann) describes an apparatus for gammairradiation and disinfection of sewage and industrial waste. Gammaradiation by itself, however, is impractical for disinfecting medicalwaste. Gamma radiation in the doses used to sterilize medical productsis considered too expensive for medical waste processing.

Besides gamma radiation, other energy sources are being considered aspotential sterilants in known systems. Microwaves are increasingly beinginvestigated for rapid sterilization of individual medical devices andshredded medical waste. Recently, an experiment showed that metallicinstruments could be disinfected in only 30 seconds in a microwave. (N.Y. Times, "Science Watch: Microwave Sterilizer is Developed," Jun. 20,1989). A problem is that this particular method can handle only a fewinstruments at a time.

According to one publication, a medical waste disposal system utilizingmicrowaves has apparently been developed. This system first shreds thewaste, sprays it with water and passes the mixture through a microwavechamber designed to raise the temperature of the mixture to 205° C.After the disinfection step, the system compresses the waste andpackages it for shipment to landfills or incinerators. (The Wall StreetJournal, p. B3, Apr. 10, 1989). One potential problem with this systemis that shredding before disinfection could release infectious particlesto the environment and may thus spread contagion. Another problem isultimate disposal of the waste: It persists in landfills or may pollutethe air when incinerated.

Further, microwaves are limited in their penetration. If applied tolarge-scale, boxed medical waste, the microwaves alone do not heat veryeffectively. In contrast, radio-frequency (R-F) waves are relativelylow-frequency waves which penetrate more effectively. Radio-frequencywaves have been used directly and indirectly for sterilization.

U.S. Pat. No. 2,114,345 (Hayford) teaches a radio-frequency applicatorwith electroscopic control for destroying bacteria in bottled beer andsimilar articles. This reference teaches an apparatus that sterilizeswith radio-frequency waves alone. Therefore, it teaches away from thecombination of radio-frequency waves with gamma radiation.

U.S. Pat. No. 3,948,601 (Fraser et al.) teaches the indirect use ofradio-frequency waves in disinfecting a wide variety of medical andhospital equipment as well as human waste. This reference teaches theuse of radio-frequency waves to heat certain gases (particularly argon)to ionize into gas plasma at approximately 100° to 500° C. Thisreferences teaches that "cool" plasma, (Col. 1, Line 12) reaches thearticle to be sterilized at a temperature of only 25° to 50° C. and verylow pressure and effectively sterilizes the article. However,sterilization by plasma gas does not suggest the direct use ofradio-frequency waves in sterilization. Reprocessing of waste andespecially medical waste is vital for several reasons. First, landfills,particularly in many urban areas, are becoming filled. In addition,older landfills may leak. Thus, burying wastes is becoming more of aproblem. Second, merely burning waste can pollute the atmosphere andcause acid rain. Current reprocessing technology should be employed toprocess medical waste for effective utilization.

What was needed before the present invention was a device to disinfector destroy the infectious potential of medical waste and to dispose ofit in a manner harmless to health care workers, waste handlers, and thepublic at large.

BRIEF SUMMARY AND OBJECTS OF THE INVENTION

The present invention provides a device for processing medicalmaterials, such as medical and veterinary waste and medical products,which disinfects or sterilizes the material by a combination of heatingand gamma radiating.

The device comprises a source of heat (for example, a source ofradio-frequency waves) to raise the internal temperature of medicalmaterials to at least about 60° C., which is sufficient to inactivatemost viruses. The device further comprises a source of gamma irradiationwhich applies a reduced dose of gamma irradiation to the medicalmaterials to complete the disinfection or sterilization process byinactivating other microorganisms, mostly bacteria.

The invention additionally comprises an apparatus for further processingof pre-sorted medical and veterinary waste either as recycled plastic oras refused-derived fuel.

Therefore, in view of the foregoing, it is a primary object of thepresent invention to disinfect medical materials by heating thematerials and exposing them to gamma radiation. A further object of theinvention is to dispose of medical and veterinary waste in anenvironmentally safe manner.

Additional objects, advantages and novel features of the invention willbe set forth in part in the description which follows, and in part willbecome apparent to those skilled in the art upon examination of thefollowing or may be learned by practice of the invention. The objectsand advantages of the invention may be obtained by means of the devicesand combinations particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of an embodiment of the invention;

FIG. 2 is a plan view of an embodiment of the invention.

DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS Disinfection

The present invention relates to a device for disinfecting medicalmaterials. By medical materials, we mean medical and veterinary waste aswell as medical products. Medical and veterinary wastes are disinfected,or rendered incapable of causing an infection. The present deviceinactivates microorganisms in medical and veterinary waste so that thewaste can no longer cause an infection. The present device can be usedto sterilize or completely kill all bacteria and viruses in, medicalproducts. Both disinfection and sterilization are accomplished throughheating and applying gamma radiation by device 1 shown in FIGS. 1 and 2.

Preliminary to the use of the present invention, medical materialarrives at a processing and recycling facility. Preferably, the materialis shipped in sealed containers. This means of shipping medicalmaterials is known in the art and has the advantages that medical wastedoes not infect its handlers and that contamination of medical productsin transit is minimized. At the facility the containers are preferablyarranged on pallets and shrink-wrapped with plastic. The pallets arethen moved into a heating chamber 10 which is capable of delivering heatby any of a variety of methods, such as radio-frequency, infrared andmicrowaves and electrical and gas radiant heating.

A preferred embodiment of this chamber is a tunnel configuration andmeans, such as a track 2, for moving the material through the tunnel.This arrangement permits the material to be gradually heated as ittravels through.

The pallets are held in the heat chamber 10 and exposed to the heatsource for a sufficient time to raise the temperature of the medicalmaterials to at least approximately 60° C. It will be recognized bythose skilled in the art that temperatures as high as 170° C. may beused without adversely affecting the process.

Next, the pallets are moved into a shielded gamma irradiation chamber20. The gamma chamber is insulated to prevent radiation from escapinginto the environment. The same type of facility that is in current usefor gamma irradiation of medical supplies may be used for this step. Forexample, a suitable gamma irradiator is Model #RT 4101, available fromRadiation Technology, Inc., Rockaway, N.J. In the chamber 20, a core ofradioactive matter (preferably cobalt 60) emerges from a liquid bath andemits ionizing radiation that is relatively constant during the periodwhen any sample is being irradiated. For subsequent loads, the time isgradually increased to account for radioactive decay of the cobalt 60.Absorbed radioactivity is measured in rads. The amount to be deliveredto medical materials is measured in megarads (Mrads), or millions ofrads. Doses may range from as little as about 0.25 Mrads to as high asabout 2.5 Mrads or more. It will be recognized by those skilled in theart that higher radiation doses will not adversely affect the process.

In one embodiment, the medical materials are moved along a trackway 2,through the heat chamber 10 and the gamma-irradiation chamber 20. Inthis arrangement, the distance from radiation sources varies but isadditive for the journey through each chamber. The total dose ofradiation to which the waste is exposed during its dwell time in thechamber is planned to provide sufficient disinfection. With a trackarrangement, the entrance and exit of the chambers are open butadditional walls are arranged to block the escape of radiation into thesurrounding areas. Such chambers are in common use for cobalt 60sterilization of medical products.

Validation

Preferably, a medical material disinfecting facility using the presentinvention is validated to assure the adequacy of the disinfectionprocess. Validation may be performed when each facility is constructedand at intervals during its operation. Validation may consist of placingheat detecting devices such as thermocouples and/or known amounts ofparticular microorganisms which are resistant to heat and to gammaradiation respectively into a maximally loaded pallet of medicalmaterials. Sufficient heat to raise the temperature of a sterilizer'sload to about 60° C. and a gamma radiation dose of about 0.50 Mrads aredelivered to the test pallet. If thermocouples are used, they should allrecord at least the minimum temperature of about 60° C. After the entiredisinfection cycle is complete, the microorganism samples are removedfrom the pallet and cultured (given nutrients and other appropriateconditions for growth) to determine survival. A typical heat-resistantmicroorganism which may be used in validation is Bacillusstearothermophilus. A typical radiation-resistant microorganism isBacillus pumilus. If more than 1 in 10,000 of either microorganismsurvives the timed cycles, the exposure to heat and/or gamma radiationis increased about 5%, or about 200,000 rads, and another pallet istested.

Device for Recycling

Another embodiment of the invention consists of starting with medical orveterinary waste that has been pre-sorted int containers of plastic andgeneral medical waste, respectively. High-grade plastics are used inmedical products and can be shredded and remolded into a variety ofproducts. This waste is subjected to heat and gamma radiation asdescribed above. Then the containers of disinfected plastic are moved toa "plastics" shredder 30. For example, an electrically powered shredderwith pneumatic ram assist and negative pressure canopy reduces medicalwaste to small particles and is available as Model Dual 1000 E fromShredding Systems, Inc., Wilsonville, Oreg. The negative pressure canopyminimizes particles entering the surrounding air. The containers areopened and the disinfected plastic is placed in the shredder andshredded to particles of about one quarter to one half inch. Thisdisinfected, shredded material is transferred into 55-gallon drums forshipment to re-users of plastic.

Likewise, the containers of disinfected general medical waste are movedto the "general medical waste" shredder. After the containers areopened, the general medical waste is placed in the shredder 30 andshredded to particles of about one quarter to one half inch. Thedisinfected waste is placed in further containers. This waste contains amixture of paper, plastic, and metal and can be used as fuel. Possibleusers include cement kilns which operate at temperatures of about 2,500°F. or more, and which would otherwise use high-sulfur coal. Because thisgeneral medical waste is low in sulfur, its use as fuel will decreasesulfur-caused acid rain.

Another preferred embodiment of this invention has a heat chamber 10which is a radio-frequency chamber having a tunnel configuration withthe following approximate dimensions: 50 feet long, 20 feet wide and 20feet high. The tunnel is lined with 3 mm-thick copper sheeting. Thecopper lining and the arrangement of the electrodes inside the tunnelare designed to confine the radio-frequency waves to the tunnel.

In the radio-frequency chamber 10, a system of exciter and groundelectrodes generate electromagnetic waves in the radio-frequency band.The radio-frequency band is between audio and infrared frequencies andcomprises approximately 10 hertz (Hz) to 300 gigahertz (GHz). When theelectrode system is supplied with electricity, it launches anelectromagnetic wave into the target medical materials.

The radio-frequency waves penetrate the pallets of medical materials.The medical materials absorb these waves whose energy is thought toproduce heat by inducing dipole rotation and molecular vibration. Whenradio-frequency waves are absorbed, they may cause differential heating.Moist articles and metal objects absorb more waves and may create "hotspots," or uneven heating. In closed containers or boxes, the steam andheat from these objects are redistributed to the entire contents of thecontainers.

The pallets are held in the radio-frequency chamber 10 and exposed toradio-frequency waves for a sufficient time to raise the temperature ofthe medical materials to at least approximately 60° C. It will berecognized by those skilled in the art that temperatures as high as 170°C. will not adversely affect the process. Preferably, the exposure toradio-frequency waves would last about 5 to 30 minutes. More preferably,the medical materials are exposed to the radio-frequency waves forapproximately 12 minutes. However, the optimal time in the chamber 10and amount of radio-frequency waves for a particular facility will varyand may be determined as described in "Validation."

Another embodiment of the invention as shown in FIG. 2 arranges theheating elements (for example, the radio-frequency generating system ofexciters and grounds) inside the gamma radiation chamber 20 forsimultaneous exposure of the medical materials to heat orradio-frequency waves and gamma radiation.

Another embodiment of the invention orients the heat or radio-frequencychamber with respect to the gamma radiation chamber so that the medicalmaterial is first exposed to gamma radiation and then heated.

Another embodiment of the invention shown in FIG. 2 employs a system oftracks and/or conveyor belts 4 to move medical or veterinary waste fromthe sterilization chambers to the shredders 30.

The foregoing descriptions of the preferred embodiments of the presentinvention have been presented for purposes of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise forms disclosed, and obviously many othermodifications and variations are possible in light of the aboveteachings. The embodiments were chosen and described to best explain theprinciples of the invention and its practical applications, therebyenabling others skilled in the art to best utilize the invention in itsvarious embodiments and with various modifications as are suited to theparticular use contemplated. It is intended that the scope of theinvention be defined by the following claims, including all equivalents.

We claim:
 1. A device for disinfecting medical materials comprising:(a)a heat source to heat the medical materials to approximately 60° C.; and(b) a source of gamma irradiation to expose the medical materials to agamma irradiation dose of approximately 0.25 to 2.0 Mrads.
 2. A devicefor disinfecting medical materials, as recited in claim 1, furthercomprising a conveying apparatus to convey the medical materials to theheat source and the gamma source.
 3. A device for disinfecting medicalmaterials, as recited in claim 1, wherein the device comprises anentrance to receive the medical materials, wherein the heat source islocated nearer the entrance than the gamma source, and wherein theconveying apparatus is between the entrance and the heat source andbetween the heat source and the gamma source.
 4. A device fordisinfecting medical materials, as recited in claim 1, wherein the gammasource comprises radioactive cobalt
 60. 5. A device for disinfectingmedical materials, as recited in claim 1, wherein the gamma sourcecomprises radioactive cesium
 137. 6. A device for disinfecting medicalmaterials comprising:(a) a source of radio-frequency waves for heatingthe medical materials to approximately 60° C.; and (b) a source of gammairradiation for exposing the medical materials to gamma radiation.
 7. Adevice for disinfecting medical materials, as recited in claim 6,further comprising a conveying apparatus to convey the medical materialsto the radio-frequency source and the gamma source.
 8. A device fordisinfecting medical materials, as recited in claim 7, wherein thedevice comprises an entrance to receive the medical materials, whereinthe radio-frequency source is located nearer the entrance than the gammasource, and wherein the conveying apparatus is between the entrance andthe radio-frequency source and between the radio-frequency source andthe gamma source.
 9. A device for disinfecting medical materials, asrecited in claim 6, wherein the gamma source comprises radioactivecobalt
 60. 10. A device for disinfecting medical materials, as recitedin claim 6, wherein the gamma source comprises radioactive cesium 137.11. A device for disinfecting and processing medical wastecomprising:(a) a heat source to heat the medical waste to a temperatureof approximately 60° C.; (b) a source of gamma irradiation capable ofexposing the heated medical waste to gamma irradiation in the range ofabout 0.25 megarads to about 2.0 megarads; and (c) a shredding apparatusto shred the medical waste.
 12. A device for disinfecting medicalmaterials, as recited in claim 11, further comprising a conveyingapparatus to convey the medical materials to the heat source, the gammasource, and the shredding apparatus.
 13. A device for disinfecting andprocessing medical waste, as recited in claim 11, wherein the shreddingapparatus comprises a particle forming apparatus for producing particlesin a size range of approximately one quarter to one half inch.
 14. Adevice for disinfecting and processing medical waste, as recited inclaim 11, wherein the gamma source comprises radioactive cobalt
 60. 15.A device for disinfecting and processing medical waste, as recited inclaim 11, wherein the gamma source comprises radioactive cesium
 137. 16.A device for disinfecting medical materials comprising:(a) a heat sourceto heat the medical materials to approximately 60° C.; and (b) a sourceof ionizing radiation capable of supplying a dose of approximately 0.25to approximately 2.0 megarads to the medical materials.
 17. A device fordisinfecting medical materials, as recited in claim 16, wherein the heatsource provides radio-frequency waves.
 18. A device for disinfectingmedical materials, as recited in claim 16, wherein the ionizingradiation source comprises a machine source of radiation.
 19. A devicefor disinfecting medical materials, as recited in claim 18, wherein saidmachine source of radiation comprises an electron accelerator.
 20. Adevice for disinfecting medical materials, as recited in claim 16,further comprising a conveying apparatus to convey the medical materialsto the heat source and the ionizing radiation source.
 21. A device fordisinfecting medical materials, as recited in claim 16, wherein thedevice comprises an entrance to receive the medical materials, whereinthe heat source is located nearer the entrance than the ionizingradiation source, and wherein the conveying apparatus is between theentrance and the heat source and between the heat source and theionizing radiation source.
 22. The device for disinfecting medicalmaterials, as recited in claim 16, further comprising a shreddingapparatus to shred the medical waste.
 23. The device for disinfectingmedical materials, as recited in claim 22, wherein the shreddingapparatus comprises a particle forming apparatus to reduce the materialsto particles in a size range of approximately one quarter to one halfinch.
 24. A device for disinfecting and processing medical wastecomprising:(a) a shredding apparatus to shred the medical waste; (b) aheat source to heat the shredded medical waste to a temperature ofapproximately 60° C.; (c) a gamma radiation source to expose the heatedmedical waste to gamma irradiation.
 25. A device for disinfectingmedical waste comprising:(a) a shredding apparatus to shred the medicalwaste; (b) a heat source to heat the shredded medical waste to atemperature of approximately 60° C.; (c) an ionizing radiation source toexpose the heated medical waste to an ionizing radiation dose ofapproximately 0.25 to 2.0 megarads.